Field
Various communication systems may benefit from parallel preamble transmissions. In particular, communication systems of the long term evolution of the third generation partnership project may benefit from methods and systems for parallel preamble transmission in power limited situations.
Description of the Related Art
The sum of total transmit (TX) power for a given user equipment (UE) is limited to a certain maximum value due to the physical limitations or regulatory requirements of the device. When the power sum of different simultaneous transmissions would exceed the threshold, a conventional UE does power scaling according to priority rules, which may—in some cases—lead to the UE completely dropping one of the transmissions. One situation in which simultaneous transmissions may take place is when the UE has overlapping random access procedures going on for a master cell group (MCG) and for a secondary cell group (SCG).
This situation can arise in long term evolution (LTE) release 12 with dual-connectivity. By contrast, in earlier releases the UE is allowed to continue only one random access procedure if a situation appears where two procedures would overlap. When MCG and SCG random access procedures overlap, UE may have to transmit overlapping preambles.
A particular issue is that while the medium access control (MAC) layer of the UE is triggering the physical (PHY) layer for preamble transmission, the MAC layer has no knowledge of the preamble powers. Therefore, the MAC layer does not know about the appearance of a power limited situation.
One way to avoid such a situation is for physical random access channel (PRACH) resources to be configured so that they never overlap in MCG and SCG. This would limit the RACH capacity, as resources would be divided between cells. Also, a certain level of synchronicity or at least knowledge of cell timings would be needed. Furthermore, dual-connectivity may need to be supported in asynchronous networks.
Semi-static power scaling would be an approach that could be used in situations where the needed maximum power of SCG preambles can be assumed to be so small that there would not be practical consequences for MCG preamble transmission if their maximum power is somewhat reduced because of the overlapping SCG preamble transmission.